The View from Below

The complex networks of life are driven by the action of microbes, simultaneously synthesizing and consuming, moving metabolites and energy with relentless, tireless efficiency. Communities of microbes are deeply interdependent, and every bacterial species depends on one or more other species for survival. The consequences of this interdependence are profound, making cooperation and collaboration at least as important as competition in the shaping of bacterial communities. The ability to synthesize a toxic protein raises some vexing challenges not only for the target cells but for the producers themselves. How, after all, can a producer strain keep from becoming the victim of its own lethal weapon? It is because that the producing cell also synthesizes an immunity protein that binds tightly to the killing domain of the bacteriocin, rendering it temporarily inactive. This safety catch will remain on until the bacteriocin is safely inside its intended target cell. The delicate balance between producer cells and target cells plays out in a surprising minuet that has been likened to the childhood game of rock-paper-scissors. A bacteriocin-producing strain emerges and acts as "paper" in our game, defeating the sensitive strain as "paper" covers "rock." Eventually, no sensitive cells survive, and only bacteriocin producers rule. But the emergence of a resistant strain from within the producer population plays the role of “scissors.” Little by little, the population shifts from bacteriocin producers to resistant cells: scissors beats paper. Yet in the absence of producers, the cost of resistance is high and the benefits nonexistent.